Wetland Reservoir Subirrigation System (WRSIS)

WRSIS Concept

A Wetland Reservoir Subirrigation System, or WRSIS for short, is an innovative agricultural water management system. WRSIS is comprised of a wetland and a water storage reservoir linked to a network of subsurface pipes used at different times to either drain or irrigate crops through the root zone. Runoff and subsurface drainage are collected from cropland into a constructed wetland. Natural processes in the wetland treat the water by removing some of the nutrients, pesticides, and sediment. The water is then routed to a storage reservoir and held until needed to subirrigate the crops during dry parts of the growing season. The storage reservoir also provides a further opportunity for sediment and adsorbed nutrients to settle out of the water. The integration of these components allows WRSIS to operate in a closed loop mode most of the time, thus restricting offsite water release (fig. 1). WRSIS can offer a number of benefits including (1) enhanced crop yields, (2) reduced offsite release of nutrients, pesticides, and sediment, (3) additional wetland vegetation and wildlife habitat, (4) more carbon sequestration in soil, and possibly, (5) decreased flooding potential downstream.

WRSIS Fact Sheet
(This PDF file contains most of the information on these pages.)

WRSIS Design

Design Considerations

There are three WRSIS demonstration sites now in operation that are located in the northwest Ohio portion of the Maumee River Basin, one each in Defiance, Fulton, and Van Wert Counties (fig. 2). All have been in operation long enough to experience seven to eight complete growing seasons. Key advantages for the Fulton and Van Wert County locations were that they already had some of the needed WRSIS infrastructure installed, including storage reservoirs and a functioning subsurface drainage system.

Map showing WRSIS test site locations.

In fields where subirrigation is planned, since the water table is to be maintained at a substantially higher level than with conventional subsurface drainage, it is often necessary to design the drain spacing using a high drainage coefficient of 38 to 51 mm (1.5 to 2 in.) per day in order to remove water from the soil quickly enough during heavy or prolonged rainfall events. The consequence of using a high drainage coefficient for design purposes is a smaller spacing between drain lines for subirrigated fields, typically 33% to 50% less than what is used in fields having only subsurface drainage. In addition to allowing faster water removal while in drainage mode, a smaller spacing is also important in providing a more uniform water distribution in the soil during subirrigation. For reasons just discussed, new drain lines at both the Fulton and Van Wert County sites were placed between the old ones already present and then integrated into the pre-existing subsurface drainage system. Control plot(s) having subsurface pipe for drainage only were included at each site for comparison with crop yields obtained through subirrigation.

Subirrigation requirements were established through model simulations with the computer program, DRAINMOD. From this, the size of the storage reservoir at the Defiance County site was determined based on the irrigation water needed for crops in eight out of every ten years. The existing reservoirs at the other two locations did not meet optimal storage requirements, however, other water sources were available which could be used for subirrigation, including a ground water well at the Van Wert County site and a local stream at the Fulton County site.

The wetland at the Van Wert County site was constructed initially to hold the 2 year, 24 hour storm event runoff and subsurface drainage from all 20 ha (50 acres) of the encompassing watershed. In northwest Ohio, a storm event of this magnitude provides approximately 66 mm (2.6 in.) of rainfall. During summer of 2003, the wetland at the Van Wert County site was re-engineering into a single wetland/reservoir complex to provide greater water storage capacity. The designed wetland storage capacities at the other two sites were somewhat less than that needed to totally capture a 2 year, 24 hour magnitude rainfall event. Should the need arise, all three locations were built with the capability to allow direct offsite release of water from either the wetland or storage reservoir. Although similar in concept, design details differ among the three WRSIS locations.

The problem and solution in regard to water table management of low elevation areas within an agricultural field.

Although similar in concept, design details differ among the three WRSIS locations. Soil conditions, topography, in-place infrastructure, etc., will all impact the final site design. Specific characteristics for each site are provided in the following sub-sections.

Defiance County

Defiance County WRSIS site schematic
The control plots with conventional drainage treatments are not shown.

Construction of the Defiance County, Ohio site occurred during June 1995, principally with volunteer contractors and donated material during an Ohio Land Improvement Contractors Association field exhibition. This location contains two 1.4 ha (3.5 acre) subirrigated fields and 8.1 ha (20 acres) of cropland with various conventional drainage treatments. Runoff and subsurface drainage are funneled into a 0.12 ha (0.30 acre) wetland having a storage capacity of 700 m³ (185,000 gal) (fig.3). A 2.4 m (8 ft) wide bench at an elevation coinciding with the permanent pool position was excavated along one side of the Defiance County wetland in spring 1999, providing additional wildlife/vegetation habitat and better water treatment capability. After detention within the wetland, water is routed through an adjacent concrete sump, containing two 0.75 kW (1 hp) submersible pumps, to a 0.16 ha (0.39 acre) reservoir having 2950 m³ (780,000 gal) of storage. Water held in the reservoir is used for subirrigation of corn and soybeans during periods when rainfall alone is not sufficient to meet crop demand. Although both subirrigated fields are down-gradient from the reservoir, a 0.37 kW (0.5 hp) submersible pump located in a concrete sump next to the reservoir is used to enhance flow rate.

Subsurface drain pipes at all three WRSIS sites were installed at a nominal depth of 0.76 to 0.91 m (2.5 to 3 ft) beneath the surface. Half of the 2.8 subirrigated hectares (7 acres) at the Defiance County site contain 10 cm (4 in.) diameter corrugated plastic tubing (CPT) drain line spaced 2.4 m (8 ft) apart, and the other half has 10 cm (4 in.) diameter CPT drains spaced 4.9 m (16 ft) apart (fig. 3). The site is mostly covered by Paulding clay (mesic Typic Haplaquepts) with some Roselms silty clay (mesic Aeric Ochraqualfs) also present. From particle size analysis of samples taken at the surface, percent sand was 0% to 11%, silt ranged from 34% to 50%, and the amount of clay was between 48% and 66%.

Saturated horizontal hydraulic conductivity values measured within the soil profile (0 to 0.8 m [0 to 2.8 ft]) with a velocity permeameter ranged from 7 x 10^-6 cm/s (0.01 in./hour) to 2 x 10^-5 cm/s (0.03 in./hour). These are dense, very low permeability clayey materials which hinder water transfer from the drain pipe to the soil during subirrigation, in turn making it difficult to maintain the target range of water table depths (25 cm [10 in.] at the drain and 46 - 51 cm [18 - 20 in.] midway between drains). In comparison to the 4.9 m (16 ft) spacing, the 2.4 m (8 ft) spacing is better adapted for consistently keeping ground water levels within the desired range, but expected crop yield increases may not be enough to offset the cost of having to install twice the amount of drain pipe. Initially, two hydraulic control structures, one for each subirrigated field, were installed to regulate ground water levels. A wet area within the northwest corner of the west subirrigated field required installation of an additional hydraulic control structure in September of 1999. By doing this, the west field is now divided into two separate zones for water table management (fig. 3). Capital costs for WRSIS construction at the Defiance County site totaled $44,700 U.S.

Fulton County

Fulton County WRSIS site schematic

The Fulton County, Ohio site has two 8.1 ha (20 acre) fields, one that is subirrigated and the other a control plot with drain pipe for subsurface drainage only (fig. 4). Drain pipes within the subirrigated field are spaced about 4.6 m (15 ft) apart, with two newer 10 cm (4 in.) diameter corrugated plastic tubing drain lines placed between each of the existing drains comprised of 10 cm (4 in.) diameter clay tile. The control plot contains only the clay tile lines and the spacing is 13.7 m (45 ft). To regulate the subirrigated field ground water levels, three hydraulic control structures were installed. This provides three separate water table management zones within the subirrigated field (fig. 4).

Subsurface drainage from both fields is routed by gravity to a 0.57 ha (1.4 acre) wetland having a storage capacity of 3790 m³ (1.0 million gal). There is very little surface runoff that enters the wetland. Water transfer between the wetland and a 0.64 ha (1.57 acre), 8706 m³ (2.3 million gal) capacity reservoir occurs via a 3.7 kW (5 hp) submersible pump or a 1.5 kW (2 hp) submersible pump, both located within an adjacent concrete sump. Either pump can also be used to route water to the field when the system is in subirrigation mode. A stream running between the wetland and reservoir provides additional water supply for subirrigation.

The Fulton County, Ohio WRSIS site was completed by local contractors during spring 1996 at a total capital cost of $60,100 U.S. Corn and soybeans are grown predominantly on Nappanee loam (mesic Aeric Ochraqualfs). From particle size analysis of samples taken at the surface, percent sand was 17% to 66%, silt ranged from 12% to 37%, and the amount of clay was between 20% and 46%. Saturated horizontal hydraulic conductivity values measured with a velocity permeameter ranged from 4 x 10^-4 cm/s (0.6 in./hour) near the surface to 7 x 10^-5 cm/s (0.1 in./hour) through the rest of the soil profile down to a depth of 1.2 m (4.0 ft).

Van Wert County

Van Wert County WRSIS site schematic

Local contractors completed Van Wert County WRSIS site construction in fall 1996 at a total capital cost of $86,300 U.S. This site has Hoytville clay (mesic Mollic Ochraqualfs) covering three 6.1 ha (15 acre) fields, two that are subirrigated, and one with buried pipe used for subsurface drainage only (fig. 5). From particle size analysis of samples taken at the surface, percent sand was 2% to 36%, silt ranged from 18% to 41%, and the amount of clay was between 47% and 56%. Saturated horizontal hydraulic conductivity values measured with a velocity permeameter ranged from 4 x 10^-4 cm/s (0.6 in./hour) near the surface to 2 x 10^-4 cm/s (0.3 in./hour) through the rest of the soil profile down to a depth of 1 m (3.3 ft).

As with all the WRSIS sites, subsurface drain pipes were installed at a nominal depth of 0.76 to 0.91 m (2.5 to 3 ft) beneath the surface. Drain lines within the two subirrigated fields have a spacing distance of 5.3 m (17.5 ft), and older 10 cm (4 in.) diameter clay tile pipe alternates with newer 10 cm (4 in.) diameter corrugated plastic tubing. The control plot has only the clay tile drain lines which are spaced 10.7 m (35 ft) apart. At the start, two hydraulic control structures, one for each subirrigated field, were installed to regulate shallow ground water levels. However, much like the Defiance County WRSIS site, a wet area in the north end of the east subirrigated field necessitated placement of an additional hydraulic control structure in June 1999. Consequently, the east subirrigated field is now partitioned into north and south zones for water table management purposes (fig. 5).

Initially, surface and subsurface drainage from all 18.2 ha (45 acres) of corn and soybean cropland were routed, via two 1.11 kW (1.5 hp) submersible pumps contained in a concrete sump, to a 0.79 ha (1.95 acre), 8710 m³ (2.3 million gal) capacity wetland and then a 1.21 ha (3.0 acre), 12870 m³ (3.4 million gal) capacity pond. In the summer of 2003, the wetland was converted to a wetland/reservoir complex comprised of a 0.36 ha (0.9 acre) wetland and a 0.85 ha (2.1 acre) reservoir. Within this complex, the wetland has a storage capacity of 3680 m³ (1 million gal), and the total reservoir storage capacity is 28330 m³ (7.5 million gal), of which 13550 m³ (3.6 million gal) can be drained by gravity. The wetland and reservoir are connected via a 30 cm (12 in.) diameter pipe with water flow regulated by a hydraulic control structure. A shallow earth embankment extending out into the wetland from its southeast corner increases the residence time of water flowing from the inlet to the outlet. By doing this, wetland effectiveness for water treatment is improved. The sump is located directly south between the wetland/reservoir complex and the pond. A 0.75 kW (1 hp) submersible pump, also located in the concrete sump, is used for subirrigation. Besides the wetland/reservoir complex and the pond, a ground water well located at the site can also supply water for subirrigation.

Water Table Management Options

The flexible use of different water table management options allows WRSIS to provide improved crop yields and potential environmental benefits. WRSIS agricultural field water tables are managed with intake pipes and hydraulic control structures. Intake pipes allow water to be added to the buried subirrigation/drainage pipe network, and in turn, the crop root zone. Hydraulic control structures contain a weir comprised of track-mounted flashboards. There are three WRSIS water table management options.

One option is uncontrolled drainage. With respect to this option, no water is supplied through the intake pipe, and all flashboards are removed from the hydraulic control structure. After a significant rainfall event, uncontrolled drainage results in the water table quickly dropping to near the level of the buried subirrigation/drainage pipe network. This option is used intermittently during the growing season to prevent crop injury due to root zone flooding. Uncontrolled drainage is used continuously, especially during portions of the fall and spring, to help site trafficability during harvest, tillage, planting, and post emergence field operations.

Schematic illustrating uncontrolled drainage.

A second option is controlled drainage. For this option, no water is supplied through the intake pipe, but flashboards are inserted or remain in place within the hydraulic control structure. If there is enough rainfall, controlled drainage allows the water table to be maintained near a level coinciding with the top of the stacked flashboards. If rainfall is not sufficient, the water table drops slowly beneath the level of the top stacked flashboard. The controlled drainage option is now being tested at the Defiance County WRSIS site during winter months to promote anaerobic conditions that decrease nitrate levels in the soil through denitrification processes, thereby limiting the amount of this nutrient/pollutant being released offsite during winter and spring months. This water table management option also has the potential to reduce organic matter biodegradation, in turn promoting soil carbon sequestration.

Schematic illustrating controlled drainage.

A third option is subirrigation. When using this option, water is supplied through the intake pipe, and flashboards are inserted or remain in place within the hydraulic control structure. Subirrigation allows the water table to be maintained near a level coinciding with the top of the stacked flashboards. The use of this option during the growing season ensures that crop water needs are completely satisfied, regardless of the prevailing climate conditions. When employed properly, subirrigation enhances crop yields, especially during dry growing seasons.

Schematic illustrating subirrigation.

Water Table Management Guidelines

The goal of proper water table management is to consistently maintain field ground water levels within an optimum range of depth beneath the ground surface, thereby minimizing plant stress by allowing crops to readily obtain water for growth, while at the same time preventing damage due to root zone flooding. During parts of the growing season, when there is a significant moisture deficit, shallow ground water levels at a WRSIS site are managed by putting water back into the soil through the subsurface drainage pipe network. Subirrigation water table depths are regulated using a weir-type hydraulic control structure placed between the drainage pipe network and its outlet (see section on water table management options). The weir, whose height governs the water table position, is comprised of a number of flashboards inserted within the control structure at its base, one on top of the other. Experience gained by subirrigating corn and soybeans at the three WRSIS sites and at two other research locations (Wooster, Ohio and Hoytville, Ohio), shows that 25 cm (10 in.) is the desired water table depth to be maintained at drain line positions. As a result of the fine-grained silt and clay soils present in northwest Ohio, typical subirrigated drain spacings of 4.6 to 6.1 m (15 to 20 ft), and a ground water level kept at 25 cm (10 in.) beneath the surface along the drain itself, the water table depths found at the midpoint between drain lines are normally between 46 and 51 cm (18 and 20 in.).

Measurement Tools for Subirrigation

Two very important tools are needed for water table management of WRSIS subirrigated fields, a rain gage and observation wells. These tools are crucial for making decisions on adding or removing flashboards from a hydraulic control structure and whether the subirrigation water supply should be continued or shut-off. The rain gage is placed in an open area adjacent to the subirrigated fields and is to be checked after each storm event. Observation wells need to be installed at several locations, including along drain lines, at midpoints between drains, and especially areas within depressions. The water level in the wells should be monitored daily to determine if the water table is at the desired depth. Small diameter observation wells work best because they respond quickly to changing ground water levels in fine-grained soils. The simple observation wells used are comprised of 2.5 cm (1.0 in.) diameter perforated PVC pipe capped at one end and wrapped along its length with a sheet of fiberglass screen taped securely in place.

Typical Procedures in the Early Growing Season

Establishing a base water table early in the growing season is essential. This makes it easier to raise ground water levels later. In northwest Ohio, the base water table is held about 15 cm (6 in.) above the outlet pipe in the hydraulic control structure beginning June 1. After all post emergence field operations are completed and the crops are at the V4 growth stage (third trifoliate leaf stage for soybeans, collar of the fourth leaf visible for corn), the ground water level can be raised for the remainder of the growing season, especially in near average or wetter years, to 25 cm (10 in.) beneath the soil surface along drain lines. This is usually done around June 15 at the Ohio WRSIS sites.

Procedures Used in the Growing Season are Based on Rainfall Amounts.

WRSIS water table management strategies are contingent on whether the growing season climate, with regard to precipitation, is wetter than average, near average, or drier than average. Determination of growing season climate by the farm manager is based on rainfall to date, and to a lesser extent, long range weather forecasts. A simplified schematic of near average, wetter, and drier growing season water table management strategies is provided in the figure below. Rainfall events, especially in near average or wetter growing seasons, often dictate that the subirrigation water supply be tuned off, and for large storms, that the hydraulic control structure flashboards be removed. After the rainfall event is over, normal subirrigation operations are not continued until the water table drops back to the desired level. A water table management strategy for dry growing seasons is still in the process of being developed. WRSIS water table management guidelines are discussed in greater detail by Allred et al. (2003).

Non-Growing Season Procedures

All WRSIS water table management discussion up this point has focused on the growing season. Typically, in the late fall, winter, and spring months (November through May), the subirrigated fields are kept in full drainage mode with flashboards removed from the hydraulic control structures and the water supply from the reservoir discontinued. This is done in large part to help site trafficability during fall harvest and tillage along with spring planting and post emergence field operations. This is not meant to imply that there are no environmental benefits provided by WRSIS between late fall and late spring. On the contrary, offsite discharge remains restricted during this period, and settlement processes in the wetland and reservoir still remove sediment and adsorbed phosphorous from water.

Perhaps a better environmental alternative for the subirrigated fields is to re-insert the hydraulic control structure flashboards to let rainfall alone bring the water table close to the surface during the months of December, January, February, and March when trafficability is not a major concern. This form of water table management is called controlled drainage and would produce anaerobic soil conditions by which excess nitrate is removed through denitrification and more carbon is sequestered due to reduced biodegradation. Winter month controlled drainage is now being tested at the Defiance County site and will require monitoring to assure that salinity build-up in the soil does not become a problem.

Environmental-Hydrologic-Hydraulic Monitoring Program

The main goal of the WRSIS project is to provide environmental benefits, particularly reductions in offsite release of nutrients and sediment, while at the same time improving crop yields. A plan for obtaining environmental, hydrologic, and hydraulic measurements along with crop yields has been implemented, but monitoring equipment installation and modification continues in order to improve data quantity and quality. These measurements are then stored and tabulated for use in optimizing the system’s design, management, and operation

The WRSIS environmental-hydrologic-hydraulic monitoring program is focused most intensively on the site in Defiance County where weather stations (Campbell Scientific, Inc. with CR10X datalogger and Spectrum Technologies, Inc. WatchDog Model 900ET), flumes (Plasti-Fab, Inc. Models H and HS), v-notch weirs, flow sensors (Isco, Inc. Model 750 Low-Profile Area-Velocity Probes, Isco, Inc. 720 Submerged Probes, Isco, Inc. 730 Bubbler Flow Modules and Scientific-Pittsburg/Panametrics Model XMT868 ultrasonic flowmeters), pressure transducers (Electronic Engineering Innovations Model 2.0/100 CM and Solinst Canada Ltd. Leveloggers and Baraolggers) and electrical capacitance monitoring loggers (Remote Data Systems Inc. Ecotone) for water level measurement, wetland/reservoir multi-level sampling masts, suction lysimeters (SOILMOISTURE Equipment Corp. Model 1900), and automatic water samplers (Isco, Inc. Model 6700) have been installed. The measurement program now in place at the Defiance County WRSIS site allows each component of the system to be monitored with regard to movement and storage of water, sediment, and nutrients in response to weather events and their corresponding wetland, reservoir, and cropland water management activities. A reduced level of monitoring occurs at the Fulton and Van Wert County locations, however, as a special consideration towards achieving the project’s overall goal, average crop yields along with weather measurement and the amount of water, sediment, and nutrients entering/leaving the wetland and released offsite are examined at all three WRSIS sites.

Implementation of the environmental-hydrologic-hydraulic monitoring program for WRSIS began in December of 1998 and continues today with new equipment installation and retrofitting of older equipment. The information collected is now being placed in a computer database. This database will over time provide a complete picture of overall system effectiveness along with guiding future design and management improvements, so that WRSIS can achieve its goal of protecting the environment, while at the same time increasing crop yields.

WRSIS Climate and Crop Yield Data

WRSIS Climate Data (1996 - 2006)

Table 1: Mean Monthly Growing Season Climate Data Averaged Over the WRSIS Sites

Month

Precip._M¹

mm (inches)

PET_M:Corn²

mm (inches)

PET_M:Soybeans²

mm (inches)

Precip._M – PET_M:Corn mm (inches)

Precip._M – ET_M:Soybeans mm (inches)

May

91 (3.6)

35 (1.4)

30 (1.2)

56 (2.2)

61 (2.4)

June

94 (3.7)

97 (3.82)

94 (3.7)

-3 (-0.1)

0 (0.0)

July

92 (3.6)

149 (5.9)

141 (5.6)

-57 (-2.2)

-49 (-1.9)

August

78 (3.1)

122 (4.8)

115 (4.5)

-44 (-1.7)

-37 (-1.5)

September

81 (3.2)

61 (2.4)

52 (2.1)

20 (0.8)

29 (1.1)

Total

436 (17.2)

464 (18.3)

432 (17.0)

-28 (-1.1)

4 (0.2)

¹ Data obtained from the NOAA - National Climate Data Center.

² Value calculated using NOAA – National Climate Data Center temperature data.

Figure 6. Average WRSIS precipitation and potential evapotranspiration (PET) data. As shown, even in an average year with regard to precipitation, there is still a substantial crop water deficit, based on PET, in the crucial growing season months of July and August.

Table 2: Total Growing Season (May 1 – Sept. 30) WRSIS Climate Data: 1996-2006

County

Year

Deviation from Average Precip.¹ mm (inches)

Precip. - PET_Corn²

mm (inches)

Precip. - PET_Soybeans²

mm (inches)

Defiance

(Weather station is in

city of Defiance, OH.)

1997

250 (9.8)

234 (9.2)

265 (10.4)

1998

3 (0.1)

-56 (-2.2)

-21 (-0.8)

1999

-130 (-5.1)

-195 (-7.7)

-161 (-6.3)

2000

70³ (2.8³)

32³ (1.3³)

65³ (2.6³)

2001

2 (0.1)

-39 (-1.5)

-6 (-0.2)

2002

-28 (-1.1)

-98 (-3.9)

-63 (-2.5)

2003

239 (9.4)

217 (8.5)

248 (9.8)

2004

176 (6.9)

156 (6.1)

188 (7.4)

2005

-88 (-3.5)

-166 (-6.5)

-131 (-5.2)

2006

69 (2.7)

24 (0.9)

56 (2.2)

Fulton

(Weather station is in

city of Wauseon, OH.)

1996

-45 (-1.8)

-48 (-1.9)

-18 (-0.7)

1997

213 (8.4)

219 (8.6)

247 (9.7)

1998

63 (2.5)

39 (1.5)

71 (2.8)

1999

-41 (-1.6)

-79 (-3.1)

-47 (-1.9)

2000

203 (8.0)

195 (7.7)

226 (8.9)

2001

42 (1.7)

14 (0.6)

45 (1.8)

2002

-153 (-6.0)

-215 (-8.5)

-182 (-7.2)

2003

151 (5.9)

142 (5.6)

172 (6.8)

2004

57 (2.2)

66 (2.6)

96 (3.8)

2005

-51 (-2.0)

-100 (-3.9)

-67 (-2.6)

2006

208 (8.2)

183 (7.2)

214 (8.4)

Van Wert

(Weather station is in

city of Van Wert, OH.)

1997

225 (8.9)

220 (8.7)

250 (9.8)

1998

68 (2.7)

5 (0.2)

41 (1.6)

1999

-108 (-4.3)

-176 (-6.9)

-141 (-5.6)

2000

174 (6.9)

147 (5.8)

179 (7.1)

2001

59³ (2.3³)

18³ (0.7³)

51³ (2.0³)

2002

-78 (-3.1)

-148 (-5.8)

-113 (-4.5)

2003

390 (15.4)

374 (14.7)

405 (15.9)

2004

299 (11.8)

302 (11.9)

334 (13.2)

2005

-49 (-1.9)

-117 (-4.6)

-82 (-3.2)

2006

71 (2.8)

39 (1.5)

71 (2.8)

¹ Equals the growing season precipitation for a particular year minus the average growing season precipitation. Data obtained from the NOAA - National Climate Data Center.

² Equals the growing season precipitation for a particular year minus that year’s calculated growing season potential crop evapotranspiration. Data obtained from the NOAA - National Climate Data Center.

³ This value may be significantly underestimated due to missing data.

Note: Total growing season evapotranspiration was determined by adding May through September monthly values calculated using the following equation:

PET_Crop =k_Ck_LPET_{Thornthwaite ,}

where Pet_Crop is the monthly potential evapotranspiration of a particular crop such as corn or soybean, k_C is a copy adjustment coefficient, k_L is a latitude adjustment coefficient and PET_Thornthwaite is the monthly potential evapotranspiration of grass based on Thornthwaite’s method.

The following scale, based on deviation from average precipitation (DAP), was used as a guage for overall growing season wetness/dryness:

extremely dry [ DAP < -114 mm (-4.5 in.)]

dry [-114 mm (-4.5 in.) < DAP < -76 mm (-3.0 in.)]

marginally dry [-76 mm (-3.0 in.) < DAP < -38 mm (-1.5 in.)]

near average [-38 mm (-1.5 in.) < DAP < 38 mm (1.5 in.)]

marginally wet [38 mm (1.5 in.) < DAP < 76 mm (3.0 in.)]

wet [76 mm (3.0 in.) < DAP < 114 mm (4.5 in.)]

extremely wet [DAP > 114 mm (4.5 in.)]

The average growing season precipitation for Defiance, Fulton, and Van Wert Counties are 434 mm (17.08), 431 mm (16.96 in.), and 445 mm (17.50 in)., respectively. The year 1996 was marginally dry in Fulton county. The 1999 growing season in the three counties ranged from marginally dry to extremely dry. The Fulton and Van Wert County sites were, respectively, extremely dry and dry in 2002. During the 2005 growing season the Defiance County site was dry, while the Fulton and Van Wert County sites were marginally dry. The Defiance County site in 2002 had a near averge growing season in regard to precipitation. All three locations were either near average or marginally wet in 1998 and 2001; and wet or extremely wet in 1997, 2000, and 2003. For 2004, the Defiance and Van Wert County sites were extremely wet, while the Fulton county site was only marginally wet. In the 2006 growing season, the Fulton County site was extremely wet, while the Defiance and Van Wert sites were marginally wet.

Table 3. WRSIS Growing Season Precipitation Classification

Year

Defiance County

Fulton County

Van Wert County

1996

-

marginally dry

-

1997

extremely wet

extremely wet

extremely wet

1998

near average

marginally wet

marginally wet

1999

extremely dry

marginally dry

dry

2000

marginally wet¹

extremely wet

extremely wet

2001

near average

marginally wet

marginally wet¹

2002

near average

extremely dry

dry

2003

extremely wet

extremely wet

extremely wet

2004

extremely wet

marginally wet

extremely wet

2005

dry

marginally dry

marginally dry

2006

marginally wet

extremely wet

marginally wet

¹Due to missing precipitation data, growing season may be wetter than indicated.

WRSIS Crop Yield Data (1996 - 2006)

Note: For the purpose of converting crop yield values between bushels/acre and kg/ha, the following values are used:

Field Corn - 1 bushels/acre = 62.86 kg/ha, and

Soybeans – 1 bushels/acre = 67.43 kg/ha.

Table 4a: Field Corn and Soybean Crop Yields (kg/ha): 1996-2006

WRSIS Site

Year

Corn (kg/ha)

Soybeans (kg/ha)

Subirrigated¹

Control²

Difference³

Subirrigated¹

Control²

Difference³

Defiance County

1997

9970

8373

1597

-

-

-

1998

8140

-

-

3621

-

-

1999

8738

7732

1006

2374

1497

877

2000

4557

4513

44

526

681

-155

2001

4803

5180

-377

1062

728

334

2002

6393

6776

-383

1585

1416

169

2003

6864

7763

-899

2434

2232

202

2004

6676

4740

1936

2003

1996

7

2005

5796

6236

-440

1537

2320

-783

2006

5129

4991

138

-

-

-

Avg.

6707

6255

289

1895

1551

94

Fulton

County

1996

11711

6839

4872

4552

3102

1450

1997

11962

10705

1257

4248

4073

175

1998

13232

11711

1521

4464

4248

216

1999

12025

8536

3489

4639

3675

964

2000

11409

10328

1081

3695

3392

303

2001

12063

4570

7493

4902

3247

1655

2002

12214

5393

6821

4005

2724

1281

2003

14615

14552

63

2562

2630

-67

2004

12698

8172

4526

4349

4045

304

2005

11610

9171

2439

-

-

-

2006

11566

10309

1257

-

-

-

Avg.

12283

9115

3168

4066

3459

607

Van Wert County

1997

9052

9322

-270

3129

3183

-54

1998

9498

10171

-673

2765

2778

-13

1999

11918

9844

2074

3506

2643

863

2000

10912

9687

1225

3581

3216

365

2001

12911

11855

1056

3634

3608

26

2002

-

-

-

4187

3007

1180

2003

-

-

-

2690

2522

169

2004

12069

11038

1031

3365

3641

-276

2005

11793

11849

-56

5064

4740

324

2006

8455

7229

1226

3270

3109

162

Avg.

10824

10127

698

3520

3243

276

¹ Average subirrigated field crop yield.

² Average control plot crop yield.

³ Difference equals subirrigated field crop yield minus control plot crop yield.

Table 4b: Field Corn and Soybean Crop Yields (bushels/acre): 1996-2006

WRSIS Site

Year

Corn (bushels/acre)

Soybeans (bushels/acre)

Subirrigated¹

Control²

Difference³

Subirrigated¹

Control²

Difference³

Defiance County

1997

158.6

133.2

25.4

-

-

-

1998

129.5

-

-

53.7

-

-

1999

139.0

123.0

16.0

35.2

22.2

13.0

2000

72.5

71.8

0.7

7.9

10.1

-2.2

2001

76.4

82.4

-6.0

15.8

10.8

5.0

2002

101.7

107.8

-6.1

23.5

21.0

2.5

2003

109.2

123.5

-14.3

36.1

33.1

3.0

2004

106.2

75.4

30.8

29.7

29.6

0.1

2005

92.2

99.2

-7.0

22.8

34.4

-11.6

2006

81.6

79.4

2.2

-

-

-

Avg.

106.7

99.5

4.6

28.1

23.0

1.4

Fulton

County

1996

186.3

108.8

77.5

67.5

46.0

21.5

1997

190.3

170.3

20.0

63.0

60.4

2.6

1998

210.5

186.3

24.2

66.2

63.0

3.2

1999

191.3

135.8

55.5

68.8

54.5

14.2

2000

181.5

164.3

17.2

54.8

50.3

4.5

2001

191.9

72.7

119.2

61.2

48.2

13.0

2002

194.3

85.8

108.5

59.4

40.4

19.0

2003

232.5

231.5

1.0

38.0

39.0

-1.0

2004

202.0

130.0

72.0

64.5

60.0

4.5

2005

184.7

145.9

38.8

-

-

-

2006

184.0

164.0

20.0

-

-

-

Avg.

195.4

145.0

50.4

60.4

51.3

9.1

Van Wert County

1997

144.0

148.3

-4.3

46.4

47.2

-0.8

1998

151.1

161.8

-10.7

41.0

41.2

-0.2

1999

189.6

156.6

33.0

52.0

39.2

12.8

2000

173.6

154.1

19.5

53.1

47.7

5.4

2001

205.4

188.6

16.8

53.9

53.5

0.4

2002

-

-

-

62.1

44.6

17.5

2003

-

-

-

39.9

37.4

2.5

2004

192.0

175.6

16.4

49.9

54.0

-4.1

2005

187.6

188.5

-0.9

75.1

70.3

4.8

2006

134.5

115.0

19.5

48.5

46.1

2.4

Avg.

172.2

161.1

11.1

52.2

48.1

4.1

¹ Average subirrigated field crop yield.

² Average control plot crop yield.

³ Difference equals subirrigated field crop yield minus control plot crop yield.

Table 5: Defiance County WRSIS Site Subirrigated Crop Yield Comparison

Between 2.4 m ( 8 ft) and 4.9 m (16 ft) Drain Line Spacings

Year

Corn - kg/ha (bushels/acre)

Soybeans - kg/ha (bushels/acre)

2.4 m Spacing

4.9 m Spacing

Difference¹

2.4 m Spacing

4.9 m Spacing

Difference¹

1997

10366 (164.9)

9574 (152.3)

792 (12.6)

-

-

-

1998

8423 (134.0)

7858 (125.0)

566 (9.0)

3466 (51.4)

3769 (55.9)

-303 (-4.5)

1999

9177 (146.0)

8298 (132.0)

880 (14)

2158 (32.0)

2583 (38.3)

-425 (-6.3)

2000

4752 (75.6)

4356 (69.3)

396 (6.3)

506 (7.5)

553 (8.2)

-47 (-0.7)

2001

5205 (82.8)

4400 (70.0)

805 (12.8)

1281 (19.0)

843² (12.5)²

438 (6.5)

2002

6757 (107.5)

6022 (95.8)

735 (11.7)

1524 (22.6)

1645 (24.4)

-121 (-1.8)

2003

7229 (115.0)

6493 (103.3)

735 (11.7)

2380 (35.3)

2488 (36.9)

-108 (-1.6)

2004

6349 (101.0)

7072 (112.5)

-723 (-11.5)

2245 (33.3)

1780 (26.4)

465 (6.9)

2005

5796 (92.2)

5796 (92.2)

0 (0.0)

1463 (21.7)

1605 (23.8)

-142 (-2.1)

2006

5475 (87.1)

4777 (76.0)

698 (11.1)

-

-

-

Average

6952 (110.6)

6462 (102.8)

490 (7.8)

1881 (27.9)

1915 (28.4)

-34 (-0.5)

¹ Difference equals 2.4 m drain line spacing crop yield minus 4.9 m drain line spacing crop yield.

² Foraging groundhogs from adjacent woodland significantly reduced yield.

Note: Subirrigated corn yields are better with a 2.4 m (8 ft) spacing between drain lines as compared to a 4.9 m (16 ft) spacing between drain lines. Conversely, subirrigated soybean yields are slightly better with a 4.9 m (16 ft) spacing between drain lines as compared to a 2.4 m (8ft) spacing between drain lines.

Table 6: Statistics on Crop Yield Differences (Subirrigated Field Minus Control Plot) in Relation to Growing Season Wetness/Dryness.

-Corn-

Near Average to Extremely Wet

Growing Seasons

-Corn-

Marginally Dry to Extremely Dry

Growing Seasons

-Soybeans-

Near Average to Extremely Wet

Growing Seasons

-Soybeans-

Marginally Dry to Extremely Dry

Growing Seasons

Mean

kg/ha (bu/ac)

1142 (18.2)

2526 (40.2)

196 (2.9)

770 (11.4)

Std. Dev.

kg/ha (bu/ac)

1923 (30.6)

2475 (39.4)

405 (6.0)

713 (10.6)

P¹

P < 2.5 %

P < 2.5 %

P < 10 %

P < 2.5 %

-Corn-

All Growing Seasons Combined

-Soybeans-

All Growing Seasons Combined

Mean

kg/ha (bu/ac)

1538 (24.5)

372 (5.5)

Std. Dev.

kg/ha (bu/ac)

2144 (34.1)

572 (8.5)

P¹

P < 0.1 %

P < 0.5 %

¹ P equals the probability that the mean value is not significantly different than zero. In the case of the data presented in this table, a low value of P indicates a high likelihood that the mean value of the subirrigated field minus control plot crop yield difference is substantially greater than zero.

Note: As of 2006, WRSIS subirrigated field copy yield increases for corn and soybeans, respectively, were 30.8% and 26.0% during drier growing seasons, 13.3% and 6.9% during near average tow etter growing seasons, and 18.1% and 13.0% overall.

WRSIS Cumulative Growing Season Rainfall and Evapotranspiration

Defiance County WRSIS Cumulative Growing Season Rainfall and Evapotranspiration

Defiance County Raw Weather Data:
http://extension.osu.edu/~usdasdru/WRSIS/defiance_county_wrsis_raw_weathe.htm

Fulton County WRSIS Cumulative Growing Season Rainfall and Evapotranspiration

Fulton County WRSIS Raw Weather Data:
http://extension.osu.edu/~usdasdru/WRSIS/fulton_county_wrsis_raw_weather.htm

VanWert County WRSIS Cumulative Growing Season Rainfall and Evapotranspiration

Van Wert County WRSIS Raw Weather Data:
http://extension.osu.edu/~usdasdru/WRSIS/vanwert_county_wrsis_raw_weather.htm

Habitat Formation

An additional benefit of the WRSIS Project, beyond water quality improvements, is the wetland habitat created as part of the water treatment system. Once constructed, no wetland species were planted at the sites. Wetland species were expected to migrate to the site from other wetlands in the proximity of the constructed wetlands. Vegetation surveys performed from 1998-2001 indicate the presence of the following wetland species: Salix exigua Nutt., Echinochloa crusgalli (L.) P. Beauv., Scirpus atrovirens Willd., Phalaris arundinaceae L., Polygonum persicaria L., Carex vulpinoidea Michx. Non-wetland species present include: Phleum pratense L., Medicago sativa L., Dactylis glomerata L. Bromus sp. and Festuca sp. (Luckeydoo, 2002). This vegetation serves as cover and breeding habitat for a diverse number of wetland species including, dragonflies (odenates), gray tree frogs (Hyla versicolor), and mallards (Anas platrhynchos).

Populations of dragonflies and damselflies are indicators of good water quality (Brown, et. al., 2000). Of the three sites, the Defiance county site has the most diverse population of dragonflies (19 species). The Fulton County site has 13 dragonfly species. This lower diversity may be due to this wetland’s distance from similar habitat and its eutrophic condition. The Van Wert site is less diverse with 9 dragonfly species.

At the Defiance county site, the algae in the wetland has been sampled for the past three years (200-2003) from early spring to late fall. Approximately 80 genera in 7 divisions have been identified to date. These divisions include: Bacillariophyta, Chlorophyta, Cryptophyta, Crysophyta, Cyanobacteria, Dinophyta, and Euglenophyta. Based on initial biovolume analysis, diatoms (Bacillariophyta) and green algae (Chlorophyta) are the dominants. Peaks in biomass occur in July and September. No significant difference (p<0.05) has been found in biomass or genera composition between the water entering the wetland and the water leaving the wetland. This may be due to the relatively small area of the wetland (0.12 ha).

Final Report 2003
An Inventory of Wildlife at Two Constructed Wetland Sites
Biology Department of the University of Findlay

Bibliography

Allred, B. J., L. C. Brown, N. R. Fausey, R. L. Cooper, W. B. Clevenger, G. L. Prill, G. A. La Barge, C. Thornton, D. T. Riethman, P. W. Chester, and B. J. Czartoski. 2003. A water table management approach to enhance crop yields in a wetland reservoir subirrigation system. Applied Engineering in Agriculture. v. 19, no. 4, pp. 407-421.

Allred, B. 2000. Innovative irrigation system implemented. Nonpoint Source News-Notes. USEPA. no. 62, October, pp. 20-23.

Allred, B. 2000. Maumee river basin project: Wetland reservoir subirrigation systems. Keeping It On The Land. Great Lakes Commision. v. 2, no. 4, pp. 1-2.

Allred, B., B. Clevenger, C. Thornton, B. Czartoski, N. Fausey, R. Cooper, L. Brown, D. Riethman, P. Chester, and H. Belcher. 2000. A novel approach to agricultural water management: Wetland reservoir subirrigation systems. Land and Water. May/June, pp. 9-13.

Richards, S. T., M. T. Batte, L. C. Brown, B. J. Czartoski, N. R. Fausey, and H. W. Belcher. 1999. Farm level economic analysis of a wetland reservoir subirrigation system in northwest Ohio. J. Prod. Agric. v. 12, no. 4, pp. 588-596.

Luckeydoo, L. M., W. B. Clevenger, and N. R. Fausey. 2004. Vegetation Establishment and Management Guidelines for Constructed Basins for Agriucultural water Treatment. Ohio State University Extension Bulletin 909. Ohio State University, Columbus, OH. 26 pages.

L. M. Luckeydoo, N. R. Fausey, and C. B. Davis. 2004. Natural recolonization in treatment basins. Land and Water. January/February, pp. 26-27.

Luckeydoo, L. M., N. R. Fausey, L. C. Brown, C. B. Davis. 2002. Early development of vascular vegetation of constructed wetlands in northwest Ohio receiving agricultural waters. Agriculture Ecosystems & Environment. v. 88, pp. 89-94.

Zucker, L. A. and L. C. Brown (Eds.) 1998. Agricultural Drainage: Water Quality Impacts and Subsurface Drainage Studies in the Midwest. Ohio State University Extension Bulletin 871. Ohio State University. Columbus, OH. 40 pages.

Photos